Void detection in foam with knit lines using THz pulse interrogation

Abstract

We model the electromagnetic interrogation of a polyurethane foam using the transverse electric (TE) mode of the two-dimensional (2D) Maxwell’s equations reduced to the wave equation for a fixed frequency in the terahertz (THz) regime. The foam block target contains knit lines which are modeled by modifying the speed of propagation, i.e., by altering the index of refraction. We describe our efforts to estimate the dielectric constant in the knit lines, as well as in the surrounding foam, by use of the classical Clausius–Mossotti equation, assuming only a change in density. We compare the numerical simulations accounting for knit lines to those in which knit lines are neglected, each in the context of modeling reflections of plane waves in foam with voids.